1. Field of the Invention
The present invention relates to television receivers or video cassette tape recorders (hereinafter called "VCR") containing a receiver for cable television (hereinafter called "CATV") signals, and more particularly to a method for reducing the reception time of a Harmonical Related Carriers (hereinafter called "HRC") mode of a CATV signal. According to the invention, HRC mode reception time can be reduced by performing Auto Fine Tuning (hereinafter called "AFT") in cases where the television receiver or VCR does not have a mode selection switch suitable for the North American CATV system.
In the HRC mode, picture carrier frequencies of all channels except channels 5 and 6 are lower by 1.25 MHz than those frequencies in standard (hereinafter called "STD") mode. The picture carrier frequencies of channel 5 and 6 are higher by 0.75 MHz than those frequencies in the STD mode. Therefore, supposing that a modulation frequency in the STD mode is fo, the corresponding frequency in the HRC mode will be fo' (=fo-1.25 MHz) (hereinafter called "fo'").
2. Description of the Related Art
U.S. Pat. No. 4,823,387 describes an improvement of tuning capabilities for scrambled channels, more particularly for tuning non-standard radio frequency (RF) signals containing scrambled video data using AFT.
Such improvements permit reception of channels being broadcast in HRC mode even by a TV receiver or VCR without a CATV mode (STD, HRC, IRC (Interval Related Carriers)) selection switch, as long as the TV receiver or VCR is provided with a CATV receiver, by performing AFT operation.
However, the AFT operation takes approximately 500-900 ms at least, and a noise is generated due to a delay time at the beginning of reception. This results in problems of poor quality for TV receivers or VCRs without CATV mode (including STD, HRC, IRC) selection switches. In cases where the TV receiver or VCR is provided with a CATV mode selection switch, the problem does not exist, but the manufacturing cost of the unit is increased.